High frequency filter

ABSTRACT

A high frequency filter having a feed-through capacitor and inductances, the latter being wound on a single magnetic core and precisely positioned relative to the capacitor.

United States Patent Kawakami et al.

[ 51 Dec. 19, 1972 HIGH FREQUENCY FILTER Inventors: Takaya Kawakami; Toshinorl Kitarnura; Yoshio Ajichi; Masayoshi Ono, all of Kyoto, Japan Assignee: Nichicon Capacitor, Limited, Kyoto,

Japan Filed: Feb. 9, 1971 Appl. No.: 1 14,010

Foreign Application Priority Data Feb. 17, 1970 Japan ..45/l5501 Feb. 17,1970 Japan ..45/1'5502 Feb. 17,1970 Japan ..4s/1s5o3 Feb. 17, 1970 Japan ..45/155 o4 U.S. Cl. ..333/79, 333/70 S, 333/78 Int. Cl. ..H03h 7/04 Field of Search ...333/79, 70, 70 S, 78; 317/101,

Primary Examiner-Herman Karl Saalbach Assistant Examiner-Marvin Nussbaum Attorney-Eugene E. Geoffrey, Jr.

[57] ABSTRACT A high frequency filter having a feed-through capacitor and indnctances, thelatter being wound on a single magnetic core and precisely positioned relative to the capacitor.

317/261, 256, 242 5 Claims, 10 Drawing Figures 10 28 1 1 II I 1 g i 1 I fl/ 1 l I l 23- /a\L 5 J 23-2a 1 l 1 20 1 1 SHEET 1 UF 3 mm a b W c 0 EAr/ J mung 2 Ir V 42 1 ll. m 4 flww xv n b 5 a u .6 A C I u u 2 2 m B n B .OIJ .01.. Q K m m c 2 1r 3 I 7.

Fig. 2 (B) (PRIOR ART) HIGH FREQUENCY FILTER This invention relates to a high frequency filter, especially an improved high frequency filter used for blocking a high frequency leakage from a pair of conductors, such as cathode heater conductors of a high frequency generator circuit including a magnetron, to which a high voltage is applied.

A conventional high frequency filter circuit consists of an inductor and a capacitor. It has been well known that a passing-through type ceramic capacitor having a conductor passing through a ceramic dielectric body is effective as the capacitor in the' case of very high frequency, and a combination of a passing-through type ceramic capacitor and an appropriate coil has been generally used as a high frequency filter in a high frequency generator circuit including a magnetron. I

In the prior high frequency filter, however, a discrete coil having a ferrite core is connected to the conductor of a passing-through type ceramic capacitor and two such units are respectively connected to the pair of conductors of the generator circuit. Such prior struc-- ture has had various disadvantages as follows: (1 interference between the both coils attached to the pair of conductors occurs sometimes and the attenuation characteristic of the filter may deteriorate at some frequency, due to difficulty of precisely positioning of the coils and the filter; (2) though the conductor between the coil and the capacitor must be as short as possible since a high frequency may be induced therein and badly affect the attenuation characteristic, this is restricted and some deterioration of the characteristic is inevitable; (3) since a large current of low frequency flows through the cathode heater circuit in a high power oscillator circuit, the ferrite core is saturated by magnetic flux produced by the coil as a result of the current and the coil inductance may be ineffective; and (4) due to its large volume, the device including this filter becomes undesirably large in size.

Therefore, a main object of this invention is to propose a novel and improved high frequency filter which overcomes the disadvantages referred to above.

This object can be attained by utilizing a novel structure of the passing-through type ceramic capacitor disclosed in a copending Japanese Patent application No. 45-1550 filed Feb. 17, 1970, entitled CERAMIC CAPACITOR. The capacitor has a dielectric body consisting of a pair of ceramic halves which are bonded together with solder or electroconductive adhesive material. The bonded surface of each half is previously provided with a plurality of inner electrodes and an outer electrode is formed on the opposite surface. A

view along the line 8-8 of FIG. 2( A);

FIG. 2(C) is a sectional front view along the line C C ofFIG. 2(A);

FIG. 3 is a frequency-attenuation chart for explaining the advantages of this invention;

FIG. 4(A) is a plan view representing another embodiment of high frequency filter according to this invention;

FIG. 4(B) is a sectional front view along the line B BofFIG.4(A);

FIG. 5(A) is a plan view representing a further embodiment of high frequency filter according to this invention;

FIG. 5(B) is a sectional front view along the line B- B ofFIG. 5(A); and

FIG. 6 is a plan view representing a fourth embodiment of a high frequency filter according to this invention.

Throughout the drawings, like reference numerals are used to denote like structural components and synthetic resin enclosures to be applied on the assemblies are only shown by dashed lines for purposes of simplifications.

Referring first to FIG. 1 representing an example of a prior art structure, the high frequency filter consists of an inductor portion 10 including a ferrite core 11 and a coil 12 wound thereon, and a capacitor portion 20 composed of a prior passing-through type ceramic capacitor. The capacitor includes a cylindrical dielectric body 21 composed of a sintered ceramic material and outer and inner electrode layers 22 and 23 formed, respectively, on the lower and upper faces thereof. A rod-shaped inner electrode terminal 24 having a flange 26 passes through'a hole formed in the center of the dielectric body 21 and the flange 26 is soldered to the inner electrode layer 23. An annular stepped outer electrode terminal 25 is soldered also to the outerv electrode layer 22. The whole capacitor assembly is enclosed within a synthetic resin as schematically shown by a dashed line 8. One end of the coil 12 is welded or soldered to the inner electrode terminal 24 of the capacitor to complete a high frequency filter unit.

In using the invention with a device such as a high frequency generator including a magnetron, two such units are to be attached respectively to a pair of conductors, but it is difficult to precisely adjust the relative positions of the both units. As described in the preface, nonuniformity of the relative positioning results in nonuniform quality of the devices due to interference and, in addition, the size of the device becomes undesirably large.

Referring now to FIGS. 2(A), 2(B) and 2(C) representing an embodiment of this invention, the high frequency filter consists of an inductor portion 10 and a capacitor portion 20. The inductor portion 10 is composed of a cylindrical ferrite core 11 and a pair of coils 12-1 and 12-2 wound commonly on the core 11 and the capacitor portion 20 is composed of a passingthrough type ceramic capacitor having novel structure claimed by the aforesaid copending patent application.

The dielectric body of this capacitor is composed of a pair of rectangular ceramic plates 21a and 21b having outer electrodes 22a and 22b respectively formed on the outer sides thereof and pairs of inner electrodes 23-1a, 23-lb, and 23-2a and 23-2b respectively formed on the inner sides thereof. The both ceramic plates 21a and 21b are bonded together with electroconductive adhesive material or solder applied to the surfaces of the inner electrodes of the both ceramic plates. Thelower ends of the coils 12-1 and 12-2 extend downwardly between the inner electrodes respectively as shown in FIG. 2(C) and electrically contacted therewith, and form the inner electrode terminals 24-1 and 24-2 of the capacitor. A pair of outer electrode terminals 25a and 25b are respectively soldered to the outer electrodes 22a and 22b and also soldered or welded to a common ground terminal 29. The whole assembly including the inductor portion is enclosed within a suitable synthetic resin as schematically shown by a dashed line 28 in the drawings.

It is evident from the foregoing discription of this invention that the relative position of the both coils 12-1 and 12-2 can be previously fixed and the relative position of the coils and the capacitor can also be adjusted precisely, as for example through the use of a suitable jig. Moreover, these relative positions are permanently fixed by the synthetic resin enclosure 28. Therefore, the filter in accordance with the invention can be manufactured with a high degree of uniformity. It is also clear that the resultant compact filter can be easily attached to the utilization circuit device and will result in a material saving in space, facilitate manufacture and reduce cost. I

Further, the filter according to this invention exhibits superior high frequency characteristics as compared with prior known filters. Referring to FIG. 3 representing frequency-attenuation characteristics, Curve 1 was plotted on a prior known filter including two .prior passing-through type ceramic capacitors each having an electrostatic capacitance of 500 'picofarads and two coils each having an inductance of 3microhenries, and Curve 2 was plotted on a filter in accordance with this invention including two parallel passing-through type ceramic capacitors each having an electrostatic capacitance of 500 picrofarads and two parallel coils each having an inductance of 2 microhenries respectively. As shown clearly in the drawing, the filter according to this invention not only exhibits a very high attenuation at high frequency, especially above 600 MHz, but also has a higher attenuation than the prior filter also at a frequency below 300 MHz.

In order to make the coil effective at a low frequency (below 400 MHz), the coil is preferably wound with a small pitch using a ferrite core but in order to make it effective at high frequency (above 500 MHz), it may be wound at large pitch or without use of ferrite core. The winding directions of the both coils are to be same, because the magnetic fluxes induced by the large low frequency currents are mutually cancelled and does not affect the inductance since the currents flow in opposite directions in the both coils, but the high frequency current flows out of the oscillator circuit through the both coils in the same direction and the magnetic fluxes are mutually added to further improve the filtering ef-' fect.

The above mentioned feature of this invention becomes more effective when the principle of this invention is applied to a high frequency filter to be used when two or more devices each of which includes a high frequency generator circuit having a magnetron are used in parallel, or when the device includes two or more high frequency generators in parallel. FIGS. 4(A) and 4( B) represent an embodimentof this invention including two pairs of coils 12-1, 12-2, 12-3, and 12-4 wound on a common ferrite core 11.

The dielectric body of the capacitor is composed of a pair of rectangular ceramic plates 21a and 21b. The ceramic plate 21a has an outer electrode 22a formed on one face thereof and four inner electrodes 23-1a, 23-20, 23-3a and 23-40 formed and arranged on the other face thereof as shown in FIG. 4(B). Similarly, the ceramic plate 21b has one outer electrode 22b and four inner electrodes (not shown). The inner electrodes on the both ceramic plates are bonded with adhesive material or solder placing the respective inner electrode conductors 24-1, 24-2, 24-3, and 24-4 extending from the coils 12-1, 12-2, 12-3, and 12-4 therebetween. Other components and arrangements are quite similar to the first embodiment shown in FIGS. 2(A) and 2(C).

FIGS. 5(A) and 5(8) represent a third embodiment of this invention which is a modification of the filter of FIGS. 2(A)-(C). This embodiment is quite similar to the first embodiment of FIGS. 2(A)-(C) except that an annular ferrite core 11 is used in place of the rodshaped one. In addition to the features described in conjunction with the first embodiment, this embodiment has an advantage resulting from the annular shape of the ferrite core 11. That is, fewer turns can be used for obtaining the same inductance as compared with a rod-shaped core, and if the core is made of material andshape having a large effective magnetic permeability, sufficient inductance can be achieved even though the coil is in the form of a straight conductor passing through the annular core and is not wound on the core.

FIG. 6 is a fourth embodiment of this invention, which is a combined modification of the second embodiment shown in FIGS. 4(A) and 4(B) and the third embodiment shown in FIGS. 5(A) and 5(8). This embodiment includes an annular ferrite core 11 and four coils 12-1, 12-2, 12-3 and 12-4 wound thereon. The structure of the capacitor portion is similar to that of the second embodiment. It is self-evident that this embodiment combines the advantages of the second embodiment with that of the third embodiment.

As described in the above, according to this invention, an improved, compact and low cost high frequency filter is provided having superior frequency characteristics and which can be manufactured using automatic procedures.

The illustrated embodiments are only presented for explanatory purposes and various modifications and changes can be made without departing from the scope of this invention. For example, the inductor portion 10 and the capacitor portion 20 may be separately manufactured and thereafter connected by welding or the like. The number of the coils, accordingly the number of the inner electrodes, can be arbitrarily selected.

However, more than eight coils are not practical and three coils or multiples thereof exhibit rather low attenuation though it isstill higher than that of prior known filters.

What is claimed is:

1. A high frequency filter comprising an inductor and a capacitor, said inductor including at least two magl060ll 0119 netically coupled coils wound in the same direction, plates. and said capacitor includingapair of ceramic dielectric 2, Th high frequency filter according to claim 1 P each Said PlateS having a single Outer 6166- wherein said coils are wound on a single magnetic core. trode layer on one face thereof and at least two inner The high frequency filt according to claim 2 electrode layers on the other face thereof, said pair of 5 ceramic dielectric plates being bonded together so that said inner electrode layers on the both ceramic dielectric plates face one another, at least two inner electrode terminal conductors placed respectively between said T t frequency accoidmg to clam] 1 inner electrode layers on the both plates and connected P Sald i and Sam capacitor are enclosed respectively to said coils, and a ground terminal con- 7 wlthm synthetlc resm nected to said outer electrodes on the both ceramic wherein said single magnetic core is rod-shaped.

4. The high frequency filter according to claim 2 wherein said single magnetic core is annular. 

1. A high frequency filter comprising an inductor and a capacitor, said inductor including at least two magnetically coupled coils wound in the same direction, and said capacitor including a pair of ceramic dielectric plates, each of said plates having a single outer electrode layer on one face thereof and at least two inner electrode layers on the other face thereof, said pair of ceramic dielectric plates being bonded together so that said inner electrode layers on the both ceramic dielectric plates face one another, at least two inner electrode terminal conductors placed respectively between said inner electrode layers on the both plates and connected respectively to said coils, and a ground terminal connected to said outer electrodes on the both ceramic plates.
 2. The high frequency filter according to claim 1 wherein said coils are wound on a single magnetic core.
 3. The high frequency filter according to claim 2 wherein said single magnetic core is rod-shaped.
 4. The high frequency filter according to claim 2 wherein said single magnetic core is annular.
 5. The high frequency filter according to claim 1 wherein said inductor and said capacitor are enclosed within synthetic resin. 